‘Vanishing colour’ may be prepared by mixing phenolphthalein with

Correct answer: dilute solution of caustic soda

Explanation: ✅ Correct Answer: C. dilute solution of caustic soda 📚 Explanation: 'Vanishing colour' can be created by mixing phenolphthalein with a dilute alkaline solution like 'caustic soda' (Sodium hydroxide). The mixture turns bright pink when it is first applied to a surface. As the solution reacts with the carbon dioxide in the air, its alkalinity decreases and the color disappears. This effect is a popular chemistry demonstration used to show the property of acid-base indicators.